davis777

What does the knock sensor do?

I had my 496 Mag standard serviced for summer and they ran the scan tool on the engine. I have 168 hours. The tech said that the Knock Sensor tripped 438 times last summer. He said that the engine was adjusting automatically for detonation..??.
I have been using 87 octaine fuel as the manual states.
R-

JIMG

check the timing. then run 89, it won't hurt anything. scan it again & see if it is still doing it.

Raylar

That much knocking in recorded events indicates a lot of engine noise! If it really is detonation, then I would guess on a 496MAG with 87 octane, that either the gas is really rot gut-not 87 octane ,the fuel system is leaning out and causing detonation, or there is a possibility one of the sensors is bad. check fuel pressure and change fuel water seperator if low and check for other codes. There is also a possibility you have internal engine noise, ie: lifter, piston slap or pin or rod noise that the knock sensors are picking up as detonation possibly. How many hours on the motor? What is your oil pressure cold and hot? Do you have any other codes in history? You should also listen carefully on the motor when it is started cold and see if you can hear any cold start up piston slap or lifter noise. This is usually when its the worst if its there. Have not really seen this condition much, especially at this frequency. You might also want to talk to Mercury technical service and get their possible input. In any event, you should probably isolate the issue and make sure its not going to do a lot of long term damage.

Good Luck

Ray @ Raylar

GOODT

raylar as usual is on the money, You can not set timming on that mtr

davis777

Thanks for the reply and the inputs.
It is a 496 Mag Standard with 168 hours on it. No other codes tripped. I do run a Corsa Diverter with internal exhuast flaps and they are very noisy and vibrate from the riser to the transom. I have changed all the water sep. fuel filter and the inline filter. Would it help to run 89 or 90 octane?
Thanks,
Robb

Raylar

Wouldn't hurt to run some 89 or 90 and see if the knock codes stop. If not go back to 87. Those diverters rattling that bad could be the noise culpret See if you can quiet them and if the codes stop you know what the problem is.

Ray @ Raylar